so will the stock mounting location allow the calipers to fit over the B-body 11.75 rotors? i have a 76 disk brake front end going on my 69 dart and would like the biggest brakes i can easily put on.
No. To swap over to 11.75" rotors you need the larger caliper brackets that came with them. They move the calipers out further to clear the larger rotors. Since you already have the later spindles and control arms (73-76), to do the swap you'll need the caliper brackets and 11.75 rotors. Some folks have also had to swap their brake hoses, but if you're using the same calipers you shouldn't have to.
Here's an article on how to identify the larger caliper brackets. They usually cost between $100 and $150 on eBay when they show up.